My application supports various files types and all of them use my custom icons assigned to them.
Only the files with extension .ini show the icon for a second when I save them and then they return to another icon.
The icon used by the system has on the left of the icon text and at the bottom in bigger font it says .ini. The text reflect the content of the file.

I have set with file-info to use my application as the default to open the files with this extension,does not help to use the icon. Double click on the file does open it with my application.
Is there an application standard to MacOs assigned to those files?
I simply can not figure out why only these files will not use my icons.
Any ideas?

If your application has been set to be the one to open a particular file type, the system will get the icon from the application bundle. How have you set up your application's Info.plist for the various file types?

If your application has been set to be the one to open a particular file type, the system will get the icon from the application bundle. How have you set up your application's Info.plist for the various file types?

Yes, the Info.plist file is ok. My 3 other file types show the right icon.
If i change the extension from ini to pni in the plist file, this icon is also fine.
There must be an application or default setting in OSX overriding my setting.
Only if I set the size of icons to very small my icon is used, if it is a bit larger the 'other' icon is used.

If you want a file to display a custom icon, different from one provided by the info.plist, look into making a QuickLook plug-in. I think they can change a file's icon, not just when doing a QuickLook.